Plastic materials are recently widely used in manufacturing optical materials, particularly, spectacle lenses because of their light weight, toughness and easiness of dyeing. Optical materials, particularly, spectacle lenses are required to have, in addition to a low specific gravity, a high refractive index and a large Abbe's number for optical properties, and a high heat resistance and a high impact resistance for physical properties. A large refractive index makes it possible to reduce the thickness of lens. A high Abbe's number reduces the chromatic aberration of lens. A high heat resistance and a high impact strength facilitate the fabrication process and are important in view of safety in use.
The inventors found a novel sulfur compound capable of providing a thin optical material having a low chromatic aberration, and filed applications for patent (Japanese Patent Application Laid-Open Nos. 9-71580, 9-110979 and 9-255781, and Japanese Patent Application No.2000-20627). The inventors further found a resin composition capable of enhancing the impact resistance, and filed applications for patent (Japanese Patent Application Laid-Open Nos. 11-292950 and 11-318960). However, the refractive index decreased with increasing impact resistance, because the component for improving the impact resistance, in turn, reduces the refractive index. Therefore, the novel sulfur compound, found by the inventors, capable of providing a thin optical material having a low chromatic aberration fails to exert its effect sufficiently in the resin composition having an improved impact resistance.